"He(Roy) has never said that he has left the party and I still believe he is a member of TMC. And to stay with the party everybody must follow its discipline which is also applicable to him," Chatterjee told reporters on the sidelines of a programme here.
"While being in the party if somebody talks like the opposition then it must be understood that the person has lost his conscience," he said.
Chatterjee's observation came a couple of days after Roy, once a close aide of party supremo and Chief Minister Mamata Banerjee, launched a fresh tirade against the party for being denied entry to Nandigram by the Trinamool Congress workers on Saturday.
Roy had also taken a dig at the industrialisation claims by the state government and alleged that all promises made to the Muslims have not been fulfilled.
Conveying a strong message to Roy, a top TMC source had recently said an eye was being kept on his picking up issues one after another to embarrass the party and the government.
Banerjee was stated to have asked the party MP Derek O'Brien to prepare a dossier on comments made by Roy time to time indicating that it would be used for taking action against him.